If you want to figure out--on your own--the amount of lye to use in your soap, you will want to use the SAP a values. A much easier way is to use the Lye Calculator.
To calculate the SAP value for a combination of oils first you need to convert all your measurements into a single unit of measure. For example. A mixture of oils consisting of 2 Lb Olive Oil, 1Lb 4oz Coconut Oil, 12oz Palm Oil will be: 32oz Olive Oil, 20oz Coconut Oil, 12oz Palm Oil.
Next you multiply each weight by the Value in the table for each oil and add them all together. This will be: 32 (0.134) + 20 (0.183) + 12 (0.144) = 9.676
Because SAP values are for sodium hydroxide in this sap table we have to make an adjustment if we are using potassuim hydroxide. To convert simply multiply the figure by 1.4.
Therefore, to produce a fully saponified soap using 2Lb (32oz) Olive Oil: 1Lb 4oz (20oz) Coconut Oil and 12oz of Palm Oil you will need 9.68oz of Sodium Hydroxide.
To superfat your soap, simply discount this figure. To create a 5% discount you multiply the amount of lye by 0.95 (95%).
For most batches of soap you will want to have between 27% and 38% of the total weight as the figure you use to determine the amount of water you are adding. So, in the above case we would figure that the minimum amount of water we want to add would be 64oz * 0.27 = 17.28 oz of water.
Metaphysical Farms offers soap making tutorials, soap recipes, a free lye calculator and recipe creation as well as homeopathy and meditation techniques to support your sustainable lifestyle
You can view the table here: http://www.metaphysicalfarms.com/pages/SAP-Table.html